Answer:

Explanation:
The volumetric expansion of the liquid is given by

where
is the coefficient of volume expansion
is the initial volume
is the change in temperature
For the liquid in this problem,

So we can solve the equation to find
:

(a) 
The radiation pressure exerted by an electromagnetic wave on a surface that totally absorbs the radiation is given by

where
I is the intensity of the wave
c is the speed of light
In this problem,

and substituting
, we find the radiation pressure

(b) 
Since we know the cross-sectional area of the laser beam:

starting from the radiation pressure found at point (a), we can calculate the force exerted on a tritium atom:

And then, since we know the mass of the atom

we can find the acceleration, by using Newton's second law:

If it's not falling through air, water, smoke, or anything else,
and gravity is the only force on it, then its speed increases
at a constant rate ... 9.8 meters per second for every second
it falls. (That's the number on Earth. It's different in other places.)
Answer:
maybe try searching it up